This project evaluates use of purified zona pellucida proteins from Baylor College of Medicine in Houston as potential immunocontraceptives in primates. Previously, three zona pellucida proteins have been evaluated. Serum from one treatment group (rec 55) was shown to significantly decrease in vitro sperm-zona pellucida binding and acrosome reactions of bound sperm. This antigen did not perturb ovarian function in immunized female macaques. Conrad has recently continued funding so that the effective protein can be tested in timed mating trials. In addition to repeating the rec-55 protein which is conjugated to protein a to increase antigenicity, rec 55-bv (grown in baclovirus) will also be tested. Twenty-four female cynomolgus macaques have been screened for normal ovarian function by monitoring urinary steroid hormone metabolites for one month. These females have been immunized and boosted monthly for 9 months. Serum titers for the zona protein rec 55-bv were elevated after 2 boosts, however the rec 55 group has not had elevated serum titers despite repeated boosting. A six month breeding trial began in the control and rec 55-bv animals only, with each female mated twice monthly to a single male near presumed time of ovulation. Females were monitored for daily menses and post-coital swabs performed to verify positive matings. After 3 months, the mating trials were stopped because half of each group (control and rec55-bv) were pregnant. The rec 55-bv immunization provided no protection against pregnancy. We are beginning sperm-zona binding experiments to determine if serum from the rec55-bv animals can prevent sperm-zona binding or subsequent acrosome reactions. Structural differences between the rec 55 and the rec 55-bv produced in the baclovirus system are being studied, to explain why this antigen was ineffective as a contraceptive vaccine. We are continuing to boost the rec 55 group and when serum titers are elevated, mating trials as described above will be performed with this group.